Recently, a hybrid vehicle and an electric vehicle are drawing a great deal of attention as an eco-friendly vehicle. Then, the hybrid vehicle is partially put into a practical use.
This hybrid vehicle is a vehicle having a DC power source, an inverter and a motor driven by the inverter as a power source in addition to a conventional engine. That is, while the power source is obtained by driving the engine, direct voltage from the DC power source is converted into alternating voltage by the inverter and the power source is obtained by rotating the motor by the converted alternating voltage. The electric vehicle is a vehicle having a DC power source, an inverter and a motor driven by the inverter as a power source.
In general, a secondary battery is installed in the hybrid vehicle or the electric vehicle as the DC power source. By demonstrating a performance of the secondary battery more, a performance of the vehicle can be improved.
For example, Japanese Patent Laying-Open No. 2005-039989 discloses an output management device for a secondary battery. In a case where the secondary battery is required to output exceeding a rated output, this output management device sets a quantity of the output and a duration time for the output based on a temperature of the secondary battery.
In general, internal resistance of a battery has dependence on the temperature. For example, the internal resistance of the battery is increased as a temperature around the battery is lowered. When the internal resistance of the battery is increased, a change in battery voltage relative to a change in electric power inputted to or outputted from the battery is increased. When the change in the battery voltage is increased, the battery voltage may exceed an upper limit value of a use range or fall below a lower limit value of the use range. However, Japanese Patent Laying-Open No. 2005-039989 does not particularly disclose such a problem.